Chapter 6 Sedimentary Rocks and Processes

These flashcards cover various key concepts related to sedimentary rocks, their formation processes, structures, and classifications.

Sedimentary Rock

Rocks formed by the accumulation and cementation of mineral and organic particles. They play a crucial role in the formation of fossil fuels, freshwater aquifers, and various building materials.

Sedimentary Rock Are Found 

Sedimentary rocks are economically
important
» Stone, concrete, silica, gypsum, iron, and
other building materials are quarried and
mined from sedimentary rocks.
» Salt is a sedimentary product.
» Fresh water is often pumped from layers
of sedimentary rock.
» Coal, oil, and natural gas are formed and
extracted from sedimentary rock.

Igneous Rock

Rocks that form when molten rock solidifies at the surface or beneath the surface.

Metamorphic Rock

Rocks that form under high temperatures and pressures, often from other types of rocks.

Limestone

A sedimentary rock mainly composed of the carbonate minerals calcite and dolomite.

Coal

An organic sedimentary rock formed from the compaction of plant material that has not completely decayed.

Sediment

(unconsolidated) particles of mineral that originate
from:
» Weathering and erosion of pre-existing rocks
(detrital sediments)
» Chemical precipitation from solution,
including secretion by organisms in water
(chemical sediments).
 Classification of sediments (detrital sediments)
based on particle size

Classification of Sediments

Gravel

Sand

Silt

Clay

Gravel 

Coarser than 2mm
» 1. Pebbles: 2-64 mm
» 2. Cobbles: 64-256 mm
» 3. Boulders: Coarser >256 mm

Sand

Grains from 1/16 mm to 2 mm

Silt

1/256 to 1/16 mm

Clay

less than 1/256 mm

Origins of Sedimentary Rocks

Sedimentary rocks originate from the accumulation and compaction of sediments derived from pre-existing rocks or organic material, often forming in layers over time.

• Lake

• Dunes

  • Reef

  • Ocean

• Glacier

  • River

  • Wind

Formation of Sedimentary Rocks

- Major processes in formation of sedimentary
Rocks:
1. Transportation
2. Deposition
3. Preservation
4. Lithification

Weathering

The process that breaks down rock into smaller particles.

Transportation

Movement of sediment away from its source, typically by water,wind, or ice, as it continue to weather

Rounding

grinding away of sharp edges
of rock fragments during transportation

Sorting

Sediments grains selected and
separated according to size, shape, or
specific gravity by agents of transportation

The sediment

size decreases with increased
transport distance.

Poorly Sorted

varying sizes
» Glaciers –poor sorters

Well Sorted

Grains nearly the same

»Rivers –good sorters

Coarse products (boulders and cobbles)

require fast moving water (mountain

streams) to be moved at all, and so are not

transported very far from their sources.

These particles may be unweathered and

retain their source mineralogy and

chemistry.

Intermediate-sized particles

(sand) are

transported by rivers and wind and

deposited at coasts or in deserts.

» Because quartz (SiO2) is abundant and

relatively resistant to chemical

weathering it makes up the bulk of sand-

sized particles

Fine particles

(silt and clay) are carried to

regions where the water is still (off-shore

environments).

» Clay minerals that are the weathering

products of feldspars and ferro-

magnesium minerals form the bulk of

these particles

Dissolved material

(Ca, Na, K, CO3, SO4,

Cl) is carried farthest and deposited where the ocean, sea, or lake is evaporated off and can precipitate as solid minerals.

Evaporites

• Calcite (CaCO3),

• Gypsum (CaSO4.2H2O),

• Halite (NaCl), and

• Sylvite (KCl)

Evaporite

Rocks formed by chemical precipitation during the evaporation of water.

Deposition

The process by which sediments accumulate and settle. This occurs when the transportation agent (such as water, wind, or ice) loses energy, causing the transported materials to come to rest. Deposition often results in the accumulation of chemical or organic sediments, typically in aquatic environments where the water is still and energy is low.

Environment of deposition

is the location in which

deposition occurs

Types Environment of deposition

• Deep-sea floor.

• Beach.

• Desert dunes.

• River channel.

• Lake bottom

Preservation

»Sediment must be preserved, as by burial

with additional sediments, in order to

become a sedimentary rock.

»but not all are preserved as they may be

eroded and transported by another agent

of erosion

Lithification

The process of converting loose sediment into solid sedimentary rock.

• Combination of compaction and

cementation – clastic texture

• Crystallization of minerals from solution – crystalline texture

Lithification

 After sediments are deposited, they are

commonly compacted by the weight of

overlying sediments.

 They may be lithified (solidified) by the

deposit of a cement or secondary mineral that

fills the pores.

 They may also be lithified by recrystallization

of the primary minerals.

Types of Sedimentary Rocks

 1. Detrital or Clastic

 2. Chemical

 3. Organic

 1. Detrital or Clastic

» Form from cemented (Lithification) sediment grains

that come from pre-existing rocks, the most common

Detrital Sediments

Sediments that originate from the physical weathering of pre-existing rocks.

 2. Chemical

» Form by precipitation of minerals from low-

temperature solution

» Have crystalline textures, held together by

interlocking crystals, no cement

 3. Organic

» Consolidation of the carbon-rich remains of plants

and animals

Inorganic

Biochemical

Conglomerate

A clastic sedimentary rock formed from rounded gravel.

Rounded gravel

» Coarse-grained

» Short, distance but

enough to round

gravel

Breccia

A clastic sedimentary rock formed from angular gravel.

angular gravel

»Coarse-grained

»Landslide deposit

»May not have travel

far

Sandstone

formed from lithification of sand sized

particles.

»Variation in mineral composition, degree of sorting,

and degree of rounding

Types of Sandstone

Quartz sandstone, Arkosic sandstone, Graywacke sandstone

Quartz sandstone,

Arkosic sandstone,

Graywacke sandstone

Clastic Sedimentary Rocks

• Shale

• Slit stone

• Clay Stone

• Mud Stone

Shale – fine-grained clastic sedimentary rock;
fissile (splits into thin layers; fractures on fine
bedding planes)

• Silt – and clay-sized grains

• Sediment deposited in lake bottoms, river deltas,floodplains, and on deep ocean floors; forms when clay minerals compact together.

Siltstone – slightly coarser-grained than shale;
non-fissile, mainly silt grains

Claystone – predominantly clay-sized grains;
non-fissile

Mudstone – silt- and clay-sized grains;
massive/blocky, non-fissile

Magma

Molten rock that forms deep beneath Earth's surface.

Erosion

The process by which sediments are transported away from their source.

Cross-bedding

A type of bedding consisting of inclined layers within a larger bed of rock.

Graded Bed

A layer with a vertical change in particle size, typically from coarse to fine.

Biochemical Sedimentary Rocks

Rocks formed from the accumulation of biological debris.

Mud-cracks

Cracks that form in fine-grained sediment as it dries and shrinks.

Ripple Marks

Features formed in sediment by the action of moving water or wind.

Bedding

Visible layers within sedimentary rock formed during deposition.

Formation

A body of rock large enough to be mappable with distinctive characteristics.